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mm: rmap: support batched unmapping for file large folios

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Similar to folio_referenced_one(), we can apply batched unmapping for file
large folios to optimize the performance of file folios reclamation.

Barry previously implemented batched unmapping for lazyfree anonymous
large folios[1] and did not further optimize anonymous large folios or
file-backed large folios at that stage.  As for file-backed large folios,
the batched unmapping support is relatively straightforward, as we only
need to clear the consecutive (present) PTE entries for file-backed large
folios.

Note that it's not ready to support batched unmapping for uffd case, so
let's still fallback to per-page unmapping for the uffd case.

Performance testing:
Allocate 10G clean file-backed folios by mmap() in a memory cgroup, and
try to reclaim 8G file-backed folios via the memory.reclaim interface.  I
can observe 75% performance improvement on my Arm64 32-core server (and
50%+ improvement on my X86 machine) with this patch.

W/o patch:
real    0m1.018s
user    0m0.000s
sys     0m1.018s

W/ patch:
real	0m0.249s
user	0m0.000s
sys	0m0.249s

[1] https://lore.kernel.org/all/20250214093015.51024-4-21cnbao@gmail.com/T/#u
Link: https://lkml.kernel.org/r/b53a16f67c93a3fe65e78092069ad135edf00eff.1770645603.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: Barry Song <baohua@kernel.org>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Baolin Wang
2026-02-09 22:07:28 +08:00
committed by Andrew Morton
parent 07f440c23a
commit a67fe41e21
1 changed files with 7 additions and 3 deletions
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10
mm/rmap.c
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@@ -1945,12 +1945,16 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio,
end_addr = pmd_addr_end(addr, vma->vm_end);
max_nr = (end_addr - addr) >> PAGE_SHIFT;
/* We only support lazyfree batching for now ... */
if (!folio_test_anon(folio) || folio_test_swapbacked(folio))
/* We only support lazyfree or file folios batching for now ... */
if (folio_test_anon(folio) && folio_test_swapbacked(folio))
return 1;
if (pte_unused(pte))
return 1;
if (userfaultfd_wp(vma))
return 1;
return folio_pte_batch(folio, pvmw->pte, pte, max_nr);
}
@@ -2313,7 +2317,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
*
* See Documentation/mm/mmu_notifier.rst
*/
dec_mm_counter(mm, mm_counter_file(folio));
add_mm_counter(mm, mm_counter_file(folio), -nr_pages);
}
discard:
if (unlikely(folio_test_hugetlb(folio))) {